Fabrics obtained by weaving warps and wefts have conventionally been used widely as an industrial fabric. They are, for example, used in various fields including papermaking wires, conveyor belts and filter cloths and are required to have fabric properties suited for the intended use or using environment. Of such fabrics, a papermaking wire used in a papermaking step for removing water from raw materials by making use of the network of the fabric must satisfy a severe demand. There is therefore a demand for the development of fabrics which do not transfer a wire mark of the fabric and therefore have excellent surface property, have enough rigidity and therefore are usable desirably even under severe environments, or are capable of maintaining conditions necessary for making good paper for a prolonged period of time. In addition, fiber supporting property, improvement in a papermaking yield, good water drainage property, wear resistance, dimensional stability and running stability are demanded. In recent years, owing to the speed-up of a papermaking machine, requirements for papermaking wires become severe further.
Since most of the demands for industrial fabrics and solutions thereof can be understood if papermaking fabrics on which the most severe demand is imposed among industrial fabrics will be described, the present invention will hereinafter be described by use of the papermaking fabric as a representative example.
An increase in the papermaking speed of a paper machine needs reinforcement of a dehydration power, because it leads to an increase in the dehydration speed. A multilayer fabric needs a drainage hole penetrating from an upper surface side layer toward a running surface side layer so that a fabric having a structure that upper surface side warps and running surface side warps, and upper surface side wefts and running surface side wefts are vertically overlapped is preferred. Misalignment of yarns constituting the upper surface side layer and yarns constituting the running surface side layer narrows a drainage hole penetrating from the upper surface side layer toward the running surface side layer, and in such a case, excessive suction must be required. When a suction force is raised, loss of fibers or fillers or bite of a wet web into a wire increases, or sticking of fibers occurs, which deteriorates wet web releasability when the wet web is transferred to a felt, or sometimes leads to remarkable generation of wire marks. In addition, owing to a high speed travel, a papermaking fabric wears gradually on a running surface side thereof, which is in contact with the machine, by the friction with a roll or the like and owing to such a phenomenon, the life of the fabric sometimes runs out. In order to improve wear resistance, a variety of measures must be taken, for example, by adopting a weft wear type design or changing the material of a yarn. It is the common practice to use a yarn with a larger diameter in order to impart the fabric with wear resistance. This measure is effective for improving the wear resistance, but not effective for attaining excellent surface property. In Japanese Patent Laid-Open No. 2001-355191, an example of undesirable overlap between upper surface side warps and running surface side warps is shown. As an example of a structure in which a long crimp of a running surface side weft is formed in a running surface side layer as illustrated in FIG. 4 of Japanese Patent Laid-Open No. 2001-355191, a 10-shaft fabric having a structure in which a running surface side weft passes over a running surface side warp, passes under a running surface side warp, passes over a running surface side warp, and passes under seven successive running surface side warps, thereby forming a long crimp can be mentioned. Transfer of yarns does not occur easily during running of the fabric, because wefts are woven twice per cycle. Since in a portion of a running surface side weft which passes over a running surface side warp, passes under a running surface side warp and then passes over a running surface side warp, however, two warps having a running surface side weft woven upward get closer toward a running surface side warp arranged therebetween. As a result, these three yarns get closer and as illustrated in FIG. 4 of Japanese Patent Laid-Open No. 2001-355191, running surface side warps are not arranged straight. Since the upper surface side warps and running surface side warps do not overlap vertically, a water draining property which papermaking fabrics must have and air permeability which fabrics for transport must have are not attained.